• Mating between males and females is boring
  • species can reproduce without sex
  • individual of species can change sex
  • species have male and female sex organs
  • some populations have only a few that mate

• Two modes of reproduction in animal kingdom
  1. Sexual:
  2. Asexual:

• Animals exhibit cycles of reproductive activity

• Mammalian reproduction is governed by hormones

• Budding:
  • found among invertebrates

• Fission:
  • about the same size
  • found among invertebrates

• Fragmentation:
  • accompanied by regeneration of lost body parts
  • sponges, worms, starfish

• Parthenogenesis:
  • found among invertebrates and vertebrates

• Sexual reproduction commonly between male and female
  • finding a partner is difficult

• Stationary animals tend to be hermaphroditic
  • individual have male and female reproductive bits
  • Any 2 individuals can mate/self-fertilize

• Sex reversal occurs in different animal phyla
  • oysters are males first, then turn to female when larger
  • the largest female in some coral fish turn to male

• Cycles controlled by hormones and environmental cues
  • occur with asexual or sexual modes
  • usually related to seasons

• Ovulation: release of eggs at midpoint of female cycle
  • cycles are variable in length, synced with seasons
  • sheep: cycle + pregnancy = birth in spring

• Daphnia: cycles between asexual and sexual
  • seasonally related to environment

• Fertilization =
  • can be external or internal

• External: eggs shed by the female & fertilized by sperm in the environment
  • moist habitat always required
  • spawning:

• Fertilization:
  • can be external or internal

• Pheromones: chemicals used to influence physiology and behavior
  • function as mate attractants
  • pheromone production in humans is controversial

• Internal fertilization produces fewer gametes
  • survival of zygotes higher

• Internal associated with protection mechanisms
  • parental care of young
  • shells, amniotic eggs, marsupials(?)

• Not just vertebrates..

• Individuals usually have gonads that produce gametes
  • essential for sexual reproduction
  • often established early in embryo development

• Many animals have complex systems
  • structures to carry, store, protect and nourish gametes
  • e.g. fruit fly (spermathecae stores sperm in female)

• Mating may occur with more than 1 male
  • males have mechanisms to prevent other male success

• Hormones coordinated from many glands/organs
  • hypothalamus, pituitary and gonads
  • endocrine system

• Gonadotropin-releasing hormone (GnRH) is secreted by the hypothalamus
  • directs release of FSH (follicle-stimulating hormone)
  • directs release of LH (luteinizing hormone)
  • both from pituitary gland

• FSH and LH act on male and female gonads
  • stimulate sex hormone production

• Gonads then produce and secrete 3 hormones
  • testosterone, estradiol and progesterone
  • found in male/females in different amounts

• Male embryos: direct reproductive structures

• Maturing mammals: induce sex characteristics
  • physical/behavior differences (male/female)

• Mature mammals: play role in gamete formation

• Some females have linked menstrual cycle
  • 10 primates, elephant shrew, some bats, spiny mouse

• Ovarian cycle:
  • series of changes in ovaries

• Menstrual cycle:
  • endometrium thickens with blood vessels
  • preparation for embryo implantation
  • if embryo does not implant, endometrium is shed

• Both cycles occur concurrently
  • use same series of hormones